Transistor with dual spacer and forming method thereof

ABSTRACT

A transistor with dual spacers includes a gate, a first dual spacer and a second inner spacer. The gate is disposed on a substrate, wherein the gate includes a gate dielectric layer and a gate electrode, and the gate dielectric layer protrudes from the gate electrode and covers the substrate. The first dual spacer is disposed on the gate dielectric layer beside the gate, wherein the first dual spacer includes a first inner spacer and a first outer spacer. The second inner spacer having an L-shaped profile is disposed on the gate dielectric layer beside the first dual spacer. The present invention also provides a method of forming said transistor with dual spacers.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to a transistor with spacers andforming method thereof, and more specifically to a transistor with dualspacers and forming method thereof.

2. Description of the Prior Art

Field effect transistors are important electronic devices in thefabrication of integrated circuits. In the conventional method offabricating transistors, a gate structure is first formed on asubstrate, and a lightly doped drain (LDD) is formed on the twocorresponding sides of the gate structure. Next, a spacer is formed onthe sidewall of the gate structure and an ion implantation process isperformed to form a source/drain region within the substrate byutilizing the gate structure and spacer as a mask. In order toincorporating the gate, the source, and the drain into the circuit,contact plugs are often utilized for interconnection purposes. Each ofthe contact plugs include a barrier layer surrounding a low resistivitymaterial to prevent the low resistivity material from diffusing outwardto other areas.

As the size of the semiconductor device becomes smaller and smaller, thefabrication of the transistors also improves and is constantly enhancedfor fabricating transistors with smaller sizes and higher quality. Forexample, the semiconductor device is enhanced through improving theshapes and the sizes of spacers, or relative positions of spacers toother elements.

SUMMARY OF THE INVENTION

The present invention provides a transistor with dual spacers andforming method thereof, which forms dual spacers, and the inner spacersof the dual spacers have L-shaped profiles, thereby the distance betweenthe source/drain and the gate can being adjusted.

The present invention provides a transistor with dual spacers includinga gate, a first dual spacer and a second inner spacer. The gate isdisposed on a substrate, wherein the gate includes a gate dielectriclayer and a gate electrode, and the gate dielectric layer protrudes fromthe gate electrode and covers the substrate. The first dual spacer isdisposed on the gate dielectric layer beside the gate, wherein the firstdual spacer includes a first inner spacer and a first outer spacer. Thesecond inner spacer having an L-shaped profile is disposed on the gatedielectric layer beside the first dual spacer.

The present invention provides a transistor with dual spacers includinga gate dielectric layer, a gate electrode, a spacer and a first dualspacer. The gate dielectric layer is disposed on a substrate. The gateelectrode is disposed on the gate dielectric layer. The spacer isdisposed on the gate dielectric layer beside the gate electrode. Thefirst dual spacer including a first inner spacer is disposed on the gatedielectric layer beside the spacer, wherein the first inner spacer hasan L-shaped profile.

The present invention provides a method of forming a transistor withdual spacers including the following steps. A gate dielectric layer anda gate electrode are formed on a substrate. A first dual spacerincluding a first inner spacer and a first outer spacer is formed on thegate dielectric layer beside the gate electrode. A second dual spacerincluding a second inner spacer having an L-shaped profile and a secondouter spacer is formed on the gate dielectric layer beside the firstdual spacer. The second outer spacer is removed.

According to the above, the present invention provides a transistor withdual spacers and forming method thereof, which forms dual spacers toadjust the distance between the source/drain and the gate, thus avoidinghigh electric field occurring between the source/drain and the gate.This improves the electrical performance. Besides, the location of asource/drain or a metal silicide can be prevented from being too closeto the gate, by disposing the inner spacers of the dual spacers havingL-shaped profiles.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-10 schematically depict cross-sectional views of a method offorming a transistor with dual spacers according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

A gate-last for high-K first, buffer layer first process is applied inthe following embodiment, but the present invention is not restrictedthereto. For simplifying the present invention, there are twotransistors presented, but the number of the transistors is not limitedthereto.

FIGS. 1-10 schematically depict cross-sectional views of a method offorming a transistor with dual spacers according to an embodiment of thepresent invention. As shown in FIG. 1, a first gate G1 and a second gateG2 are formed on a substrate 110. The substrate 110 may be asemiconductor substrate such as a silicon substrate, a siliconcontaining substrate, a III-V group-on-silicon (such as GaN-on-silicon)substrate, a graphene-on-silicon substrate or a silicon-on-insulator(SOI) substrate. The substrate 110 may include a first area A and asecond area B. In this embodiment, a first gate G1 is located in thefirst area A while a second gate G2 is located in the second area B, andthe first area A is an active area of a low voltage transistor such as alogic circuit active area while the second area B is an active area of ahigh voltage transistor, thereby the first gate G1 being a gate of a lowvoltage transistor while the second area B being a gate of a mediumvoltage transistor, but it is not limited thereto. Thus, the size of thefirst gate G1 is less than the size of the second gate G2, and a widthW1 of the gate channel of the first gate G1 is less than a width W2 ofthe gate channel of the second gate G2, but it is not limited thereto.

More precisely, the steps of forming the first gate G1 and the secondgate G2 having different sizes may include the following. An isolationstructure 10 may be formed in the substrate 110 by etching andlithography processes. In this embodiment, the isolation structure 10may be a shallow trench isolation (STI) structure, which may be formedthrough a shallow trench isolation process, and the forming method isknown in the art, and will not be described herein, but it is notlimited thereto. In another embodiment, the isolation structure 10 maybe a field oxide (FOX) structure, but it is not limited thereto.

A recess R1 may be optionally formed in the substrate 110 of the secondarea B, and then a gate dielectric layer 120 blanketly covers thesubstrate 110 of the first area A and the second area B, thereby athickness t1 of the gate dielectric layer 120 in the first area A isless than a thickness t2 of the gate dielectric layer 120 in the secondarea B. By doing this, the gate dielectric layer 120 has a flat topsurface S1. The gate dielectric layer 120 may be formed by an in-situsteam generation (ISSG) process or a thermal oxide process, but it isnot limited thereto. In another embodiment, a dielectric layer havingcommon thicknesses in the first area A and the second area B is formedblanketly, and then the dielectric layer in the first area A ispartially removed or thinned down, therefore a dielectric layer (notshown) having a thickness in the first area A thinner than a thicknessin the second area B being formed. Thereby, a dielectric layer havingdifferent thicknesses in the first area A and the second area B can beformed.

As shown in FIG. 1, a first gate electrode E1 and a second gateelectrode E2 are respectively formed on the gate dielectric layer 120 ofthe first area A and on the gate dielectric layer 120 of the second areaB. Thus, the gate dielectric layer 120 protrudes from the first gateelectrode E1 and the second gate electrode E2 and covers the substrate110. More precisely, the first gate electrode E1 may include adielectric layer having a high dielectric constant 122 a, a sacrificialelectrode layer 124 a and a cap layer 130 a stacked from bottom to top,and the cap layer 130 a may include a nitride layer 132 a and an oxidelayer 134 a stacked from bottom to top; the second gate electrode E2 mayinclude a dielectric layer having a high dielectric constant 122 b, asacrificial electrode layer 124 b and a cap layer 130 b stacked frombottom to top, and the cap layer 130 b may include a nitride layer 132 band an oxide layer 134 b stacked from bottom to top, but it is notlimited thereto. Methods of forming the dielectric layer having a highdielectric constant 122 a/122 b, the sacrificial electrode layer 124a/124 b and the cap layer 130 a/130 b may include the following. Adielectric layer having a high dielectric constant (not shown), asacrificial electrode layer (not shown) and a cap layer (not shown) aresequentially stacked on the gate dielectric layer 120 of the first areaA and the second area B, and then the cap layer (not shown), thesacrificial electrode layer (not shown) and the dielectric layer havinga high dielectric constant (not shown) are patterned to form the firstgate electrode E1 and the second gate electrode E2.

A spacer 142 a/142 b is formed on the substrate 110 (the gate dielectriclayer 120) beside the first gate G1 and the second gate G2 respectively.The spacer 142 a/142 b may be a single layer or a multilayer constitutedby materials such as silicon nitride or silicon oxide etc. In thisembodiment, the spacer 142 a/142 b is a single nitride spacer. A lightlydoped ion implantation process may be performed to form a lightly dopedsource/drain 144 a/144 b in the substrate 110 beside the spacer 142a/142 b respectively. The lightly doped source/drain 144 a and thelightly doped source/drain 144 b may be doped respectively dependingupon required concentrations, and the locations of the lightly dopedsource/drain 144 a and the lightly doped source/drain 144 b depend uponthe spacer 142 a and the spacer 142 b. Dopants of the lightly doped ionimplantation process may be trivalent ions such as boron or pentavalentions such as phosphorum, depending upon the electrically types of thefirst gate G1 and the second gate G2. In this case, the first gate G1and the second gate G2 have common conductive types, but differentsizes, thus the lightly doped source/drain 144 a and the lightly dopedsource/drain 144 b having common conductive types, but may havingdifferent kinds of ions or different concentrations of ions. In anothercase, the first gate G1 and the second gate G2 have different conductivetypes.

Please refer to FIGS. 2-3, a first dual spacer 150 a/150 b is formed onthe gate dielectric layer 120 beside the gate electrode E1/E2respectively. In this embodiment, the first dual spacer 150 a and thefirst dual spacer 150 b may have common spacers having common sizes andthicknesses, and may be formed at the same time. In another embodiment,the first dual spacer 150 a and the first dual spacer 150 b may bedifferent spacers and may be formed respectively. The first dual spacer150 a or the first dual spacer 150 b may be a single layer or amultilayer constituted by materials such as silicon nitride or siliconoxide etc. In this case, the first dual spacer 150 a includes a firstinner spacer 152 a and a first outer spacer 154 a while the first dualspacer 150 b includes a first inner spacer 152 b and a first outerspacer 154 b, and the first inner spacer 152 a and the first innerspacer 152 b have L-shaped profiles, but it is not limited thereto.Preferably, the first inner spacer 152 a/152 b is an oxide spacer, andthe first inner spacer 152 a/152 b therefore has different material fromthe spacer 142 a/142 b, which is a single nitride spacer, thereby thefirst inner spacer 152 a/152 b and the spacer 142 a/142 b have etchingselectivity. Similarly, the first outer spacer 154 a/154 b is preferablya nitride spacer, for the first outer spacer 154 a/154 b havingdifferent material from the first inner spacer 152 a/152 b, thereby thefirst inner spacer 152 a/152 b and the first outer spacer 154 a/154 bhave etching selectivity, but it is not limited thereto.

More precisely, a first inner spacer material 152 and a first outerspacer material 154 are formed to blanketly cover the gate dielectriclayer 120, the gate electrode E1 and the gate electrode E2, and then thefirst inner spacer material 152 and the first outer spacer material 154are etched to form the first dual spacer 150 a and the first dual spacer150 b at the same time, wherein the first dual spacer 150 a and thefirst dual spacer 150 b both have L-shaped profiles.

As shown in FIG. 4, a second inner spacer material 162 and a secondouter spacer material 164 are formed to blanketly cover the gatedielectric layer 120, the gate electrode E1 and the gate electrode E2.In this embodiment, the second inner spacer material 162 is an oxidelayer while the second outer spacer material 164 is a nitride layer, butit is not limited thereto. Methods of forming the second inner spacermaterial 162 and the second outer spacer material 164 may be usingstress memorization technique (SMT), therefore the second outer spacermaterial 164 is a stress material layer.

As shown in FIGS. 5-6, only the second outer spacer material 164 and thesecond inner spacer material 162 in the second area B is etched, therebya second dual spacer 160 b being formed in the second area B. As shownin FIG. 5, a photoresist P1 covers the first area A and exposes thesecond area B. As shown in FIG. 6, the second outer spacer material 164and the second inner spacer material 162 in the second area B are etchedto only form the second dual spacer 160 b in the second area B, and topreserve a second inner spacer material 162 a and a second outer spacermaterial 164 a in the first area A. Thereafter, the photoresist P1 isremoved. The second dual spacer 160 b may include a second inner spacer162 b and a second outer spacer 164 b, and the second inner spacer 162 bhas a L-shaped profile.

The gate dielectric layer 120 of the second area B is also etched andthus is thinned to become a gate dielectric layer 120 a while the secondouter spacer material 164 and the second inner spacer material 162 ofthe second area B are etched. Thus, the gate dielectric layer 120 aprotruding from the second gate electrode E2 may at least include afirst part K1 and a second part K2, wherein the first part K1 is locatedright below the second inner spacer 162 b and the second part K2(meaning the exposed part of the gate dielectric layer 120 a) isuncovered by the second inner spacer 162 b. Since the second part K2 isthinned down while the second outer spacer material 164 and the secondinner spacer material 162 in the second area B are etched. Therefore, athickness t3 of the first part K1 is larger than a thickness t4 of thesecond part K2.

As shown in FIG. 7, a photoresist P2 covers the first area A and exposesthe second area B, and then an ion implantation process is performed toform a source/drain 166 in the substrate 110 beside the second dualspacer 160 b in the second area B. Dopants of the ion implantationprocess may be trivalent ions such as boron or pentavalent ions such asphosphorum, depending upon the electrically type of the second gate G2.Thereafter, the photoresist P2 is removed.

Then, the second outer spacer 164 b is removed and the second innerspacer 162 b is preserved, as shown in FIG. 8. In this embodiment, thesecond outer spacer material 164 a of the first area A is removed whilethe second outer spacer 164 b of the second area B is removed, but thesecond inner spacer material 162 a is still preserved.

As shown in FIG. 9, a salicide process may be performed to form a metalsilicide 166 a on the source/drain 166 after the second outer spacer 164b of the second area B is removed. Since the first part K1 of the gatedielectric layer 120 a of FIG. 8 is preserved, the metal silicide 166 acan be restrained and only be formed beside the first part K1 withoutextending to the substrate 110 right below the first part K1 because ofthe thickness t3 of the first part K1 being thick enough. Meanwhile, thethickness t4 of the second part K2 is also thin enough for the metalsilicide 166 a being formed in the second part K2.

After the metal silicide 166 a is formed on the source/drain 166, thefirst outer spacer 154 b is removed but the first inner spacer 152 b ispreserved, as shown in FIG. 10. In this embodiment, the first outerspacer 154 a in the first area A is removed while the first outer spacer154 b in the second area B is removed, the first inner spacer 152 a inthe first area A is reserved, and a gate dielectric layer 120 b isformed.

The sacrificial electrode layer 124 a and the cap layer 130 a of thefirst gate electrode E1, and the sacrificial electrode layer 124 b andthe cap layer 130 b of the second gate electrode E2 may be removed whilethe first outer spacer 154 a of the first area A and the first outerspacer 154 b of the second area B are removed. Then, a first metal gateM1 and a second metal gate M2 fill respectively to replace the firstgate electrode E1 with the first metal gate M1 and to replace the secondgate electrode E2 with the second metal gate M2, wherein a metal gatereplacement process is well known in the art and is not describedherein. Thereafter, a contact etch stop layer 170 may entirely cover anddirectly contact the first inner spacer 152 a and the first inner spacer152 b.

As shown in FIG. 10, the gate dielectric layer 120 b protruding from thesecond metal gate M2 at least includes a third part K3 and a fourth partK4, wherein the third part K3 is located right below the first innerspacer 152 b, but the fourth part K4 is uncovered by the first innerspacer 152 b. Since the fourth part K4 in thinned down while the secondouter spacer 164 b of the second area B is removed, a thickness t5 ofthe third part K3 is larger than a thickness t6 of the fourth part K4.By doing this, the fourth part K4 is located between the source/drain166 and the first inner spacer 152 b. In other words, the distancebetween the source/drain 166 and the second metal gate M2 can beadjusted by forming the spacer 142 b, the first dual spacer 150 b andthe second dual spacer 160 b.

To summarize, the present invention provides a transistor with dualspacers and forming method thereof, which forms a second dual spacerbeside a second gate to adjust the distance between the source/drain andthe gate, thus avoiding high electric field occurring between thesource/drain and the gate. This improves the electrical performance.Besides, the location of a source/drain or a metal silicide can beprevented from being too close to the gate, by disposing the innerspacer of the second dual spacer having a L-shaped profile. Moreover,the gate dielectric layer of the present invention entirely covers thesubstrate, so that the gate dielectric layer can have multi partialthicknesses through the etchings of spacers. Hence, the metal silicidecan be formed and the forming regions of the source/drain and the metalsilicide can be restrained.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A transistor with dual spacers, comprising: agate disposed on a substrate, wherein the gate comprises a gatedielectric layer and a gate electrode, and the gate dielectric layerprotrudes from the gate electrode and covers the substrate; a first dualspacer disposed on the gate dielectric layer beside the gate, whereinthe first dual spacer comprises a first inner spacer and a first outerspacer; a second inner spacer having an L-shaped profile disposed on thegate dielectric layer beside the first dual spacer, wherein the gatedielectric layer protruding from the gate electrode comprises a firstpart and a second part, wherein the first part is right below the secondinner spacer, and the second part is uncovered by the second innerspacer, wherein a thickness of the first part is larger than a thicknessof the second part; and a source/drain disposed in the substrate besidethe second inner spacer, wherein the second part vertically overlaps thesource/drain completely.
 2. The transistor with dual spacers accordingto claim 1, wherein the substrate has a recess, and the gate dielectriclayer is disposed in the recess.
 3. The transistor with dual spacersaccording to claim 1, further comprising: a spacer disposed on thesubstrate between the gate and the first dual spacer; and a lightlydoped source/drain disposed in the substrate beside the spacer.
 4. Thetransistor with dual spacers according to claim 1, further comprising: afirst gate disposed on the substrate, wherein the gate is a gate of amedium voltage transistor while the first gate is a gate of a lowvoltage transistor, and the second inner spacer having the L-shapedprofile is only disposed on the substrate beside the gate.
 5. Atransistor with dual spacers, comprising: a gate dielectric layerdisposed on a substrate; a gate electrode disposed on the gatedielectric layer; a spacer disposed on the gate dielectric layer besidethe gate electrode; a first dual spacer comprising a first inner spacerdisposed on the gate dielectric layer beside the spacer, wherein thefirst inner spacer has an L-shaped profile, the gate dielectric layerprotrudes from the gate electrode, and the gate dielectric layercomprises a third part and a fourth part, wherein the third part isright below the first inner spacer, and the fourth part is uncovered bythe first inner spacer, wherein a thickness of the third part is largerthan a thickness of the fourth part; and a source/drain disposed in thesubstrate beside the first inner spacer, wherein the fourth part isbetween the source/drain and the first inner spacer.
 6. The transistorwith dual spacers according to claim 5, wherein the substrate has arecess, and the gate dielectric layer is disposed in the recess.
 7. Thetransistor with dual spacers according to claim 5, further comprising: alightly doped source/drain disposed in the substrate beside the spacer.